Hello All,
I have found the answers to my questions. I have shared my finding below. Hope it helps.
If you have a none SAP backend and there is a OData service from this backend, then NetWeaver Gateway can directly consume it as discussed in the below link:
External OData service - http://help.sap.com/saphelp_gateway20sp06/helpdata/en/a6/d52d733971414a9fdf6cf188dc9059/frameset.htm
If there is no OData service from the Non-SAP backend, we need to define a Backend Operation proxy (BOP) to consume the Web Service from the Non-SAP backend as discussed in the below link:
http://help.sap.com/saphelp_gateway20sp06/helpdata/en/64/472d8e21a342ba9d83e403ff4cd9db/frameset.htm
BR
Abhishek